Sulfonates are a class of chemicals used in household, industrial, and institutional cleaning applications, personal care and agricultural products, metalworking fluids, industrial processes, emulsifying agents, corrosion inhibitors and as additives in lubricating oils. Some of the desirable properties of sulfonates for use in lubricating oil applications include their low cost, compatibility, water tolerance, corrosion inhibition, emulsion performance, friction properties, high temperature stability, rust performance, and light color.
Sulfonates that are used in lubricating oil applications have been classified as either neutral sulfonates, low overbased (LOB) sulfonates, or high overbased (HOB) sulfonates. In the past, natural sulfonates, made as a by-product of white oil and process oil production, dominated the sulfonate market. However, as refineries switched to hydrotreating processes, which gave improved yields of process oils and white oils, and as the desire for higher utilization of raw materials and thus improved economics grew, synthetic sulfonates have became more readily available. Synthetic sulfonates now have a major market and have been prepared from synthetic sulphonic acids which have in turn been prepared for example by the sulphonation of C12 to C60+ alkyl substituted benzene, or xylene or toluene compounds and mixtures thereof. It has been found that same synthetic sulphonic acids are difficult to neutralize, for example magnesium hydroxide or lime, to produce sulfonates which have acceptable properties; the attempted neutralization results in the production of gelatinous products which for example can be solid at room temperature. Many synthetic sulfonates have been produced from sulfonated polyalkyl aromatic compounds; see for example U.S. Pat. No. 4,764,295. Numerous methods and compositions have been developed to improve the overall viscometric property of these sulfonates, see for example U.S. Pat. Nos. 5,939,594, 6,054,419 and 6,204,226.
Polyalkenyl sulfonates and processes for their preparation are known in the art. U.S. Pat. No. 3,954,849 discloses a two step process for preparing a mixture of alkenyl sulfonic acids wherein the alkenyl group is a propene or butene polymers having a number average molecular weight of 250 to 500. U.S. Pat. No. 4,105,647 discloses a process for sulfonating polymers which are prepared by solution polymerization using Friedel-Crafts of Ziegler-type catalyst. U.S. Pat. No. 4,157,432 discloses of a sulfonation process employing homopolymers and copolymers which may contain a high level of olefinic unsaturation, typically internal unsaturation in the polymer backbone. U.S. Pat. No. 6,410,491 discloses a method for making a polyalkenyl sulfonates wherein the polyalkenyl sulfonic acid is derived from a mixture of polyalkene comprising greater than 20 mole percent alkyl vinylidene and 1,1-dialkyl isomers and polyisobutene sulfonates derived therefrom. U.S. Pat. Nos. 6,632,781 and 7,012,045 disclose particular applications which employ this polyisobutenyl sulfonate. The degree of reactivity, oil solubility, detergeney effect and viscosity behavior are influenced by the polyisobutene characteristics. The high percent alkyl vinylidene polyisobutene of U.S. Pat. No. 6,430,491 is typically made with a BF3 catalyst and commonly contains a polydispersity of about 1.65 to about 2.0. Thus, these polyisobutylenes (although containing a high proportion of reactive end groups) contain a range of molecular weights within the distribution. The large molecular weight distribution is a consequence of the polyisobutene reaction type and leads to a comparatively high molecular non-uniformity of these polyisobutene sulfonates, it has been showed herein, that this relatively large molecular weight distribution (range of low molecular weight to high molecular weight polyisobutenyl sulfonate) impacts the overall viscosity behavior and low temperature viscosity performance. Polyisobutenyl sulfonates having a relatively narrow distribution of molecular weight and have a high methyl-vinylidene end group may be prepared for example by cationic quasi-living polymerization of isobutene.
The present invention is directed in part to the unexpected discovery that polyisobutene sulfonates having a high proportion of reactive end groups and having a relatively narrow molecular weight distribution lead to improved viscometrics, particularly in kinematic viscosity (kv), intrinsic viscosity, and in low temperature performance such as that demonstrated in the cold, cranking simulator (CCS).